The pair of prime ministerial contenders are understood to have held late-night talks
Boris Johnson and Rishi Sunak were said to be locked in talks late into the evening as speculation mounted over whether the pair could strike a deal to lay the foundations for a unified Conservative government.
Mr Johnson was lagging behind his former chancellor in public support from MPs as Mr Sunak gained a valuable ally in Kemi Badenoch on Saturday, with backers of the ex-PM challenged over claims he had reached the number required to secure a spot on the Tory ballot paper.
Sir James Duddridge, a friend of Mr Johnson, said the former prime minister had the support of the 100 MPs required to reserve his place in the vote.
But Sunak supporter Richard Holden cast doubt on this suggestion, arguing that the equivalent number of public declarations had not been made “because they don’t exist”.
As the day drew to a close, neither Mr Johnson nor Mr Sunak had declared their candidacy, with reports suggesting the pair held talks in the evening to agree on a joint ticket.
In a blow to Mr Johnson’s campaign should he decide to seek a second stint in Downing Street, International Trade Secretary and former leadership contender Ms Badenoch threw her weight behind the ex-chancellor, insisting it was not the time for “nostalgia for the cavalier elan of 2019”.
She admitted she had “on occasion” been a member of “the Boris Johnson fan club”, but she said the Tories are not “organising a popularity contest”, and stressed the party is “not a vehicle for any one individual’s personal ambitions”.
Mr Johnson has returned to the UK to plot a second run for the top job, in a move that has divided opinion among Conservative MPs including his former allies.
He arrived at Gatwick Airport on Saturday morning with his family after breaking off from a holiday in the Dominican Republic following Liz Truss’s dramatic resignation on Thursday.
Meanwhile, an ally of former home secretary Suella Braverman told the PA news agency she had been personally “heavily courted” by both Mr Johnson and Mr Sunak and was likely to decide who to back for the Tory leadership on Sunday.
Despite being the only candidate to declare so far, Cabinet minister Penny Mordaunt is far behind her potential rivals on public support from MPs, with just 21 to Mr Johnson’s 44 and Mr Sunak’s 113, according to a PA tally.
Setting out her plan to “unite the party and the country” in the Express, she warned the Tories had “let ourselves become distracted by internal disputes”.
Ms Mordaunt used her pitch to stress the need to “make Brexit work”, “focus on the potential of all our citizens” and “defend our Union and its territorial integrity”, pledging her support for reforming the controversial Northern Ireland Protocol.
She insisted she is not seeking the top job for an “easy ride”, and vowed to build a government which “draws from all our best talent”.
Writing in the Sunday Times, Ms Badenoch said her party must remind people that “Conservatives care about the country, not ourselves”.
The International Trade Secretary suggested Mr Sunak would bring a “disciplined approach” to Government, citing his “fiscal conservativism” and stressing that “right now, being able to say no is what we need”.
She said everyone in the party will need to make “sacrifices” to prove to people the Tories can “unite”.
For her, this means refraining from a second leadership bid, she said, while some will have to forsake a job in government under their preferred candidate “so that others can be brought into the tent”.
Mr Johnson’s potential return has divided opinion even among his allies in the parliamentary party, including his former deputy prime minister and foreign secretary Dominic Raab.
Mr Raab said “we cannot go backwards” and pointed out the ex-PM faces an investigation into his actions over partygate.
He backed Mr Sunak, saying he was “very confident” the former chancellor would stand.
Moments after Mr Johnson landed back in the UK on Saturday, ex-home secretary Priti Patel said he had her support – but his potential bid suffered a setback as former close allies Steve Barclay and Lord Frost urged colleagues to back Mr Sunak.
Mr Johnson’s father Stanley predicted that his son would put his name forward and beat Mr Sunak in a head-to-head contest.
The former PM has so far won the support of six Cabinet ministers: Ben Wallace, Jacob Rees-Mogg, Simon Clarke, Chris Heaton-Harris, Alok Sharma and Anne-Marie Trevelyan.
But his public endorsements fell far short of those for Mr Sunak.
Another supporter of the ex-PM, ex-culture secretary Nadine Dorries, said in a contest between Mr Johnson and Mr Sunak “only Boris is a proven winner”, adding that if the former chancellor was instead chosen, “we would enter unchartered and potentially dangerous waters”.
Writing in The Mail on Sunday, Ms Dorries added: “Any Tory MP who votes for Rishi Sunak tomorrow will be taking a risk with the future of the party.
“If he is chosen, power would be transferred out of the hands of the people who exercised their choice at the ballot box less than three years ago and placed into their own very privileged and already powerful hands.
“That would be an untenable and undemocratic position for us to be in. If that happens, I have no idea how we would be able to look voters in the eye and deny them a General Election that Labour is screaming out for…
“A Tory Party led into the next Election by anyone other than Boris Johnson would mean the country would be looking into the face of a Socialist government.”
In the same newspaper, the former Brexit secretary and Sunak-backer David Davis said the “root of many” of the Tories’ problems was that the last two prime ministers had chosen Cabinets “almost exclusively from a narrow group of cronies they thought they could dominate”.
Tory MPs will vote on Monday, and two candidates will be put forward to the party membership unless one pulls out, with a result being announced on Friday.
Candidates have until 2pm on Monday to secure the 100 nominations, limiting the ballot to a maximum of three candidates.
Supporters of Mr Johnson believe that if he can make it to the last two, he will win in the final online ballot of party activists with whom he remains hugely popular.
Some MPs have warned they would resign the Tory whip and sit in the Commons as independents if Mr Johnson returned to Downing Street.
Meanwhile, Conservative Party chairman Sir Jake Berry joined the Business Secretary and Johnson-supporter Mr Rees-Mogg in calling for the vote to be decided by members rather than MPs.
The Tory chairman told the Telegraph the party’s future was in the grip of an “existential crisis” and if the Tories believed in democracy, “members cannot be denied a say on who the next leader of the party is”.
He added: “We have seen two Prime Ministers in a row effectively removed from office by MPs despite the fact that they have won the membership.
“I fear that it might be a point where members think ‘what is really the point of being a member of the Conservative party’.
“Politics is not delivered in this country by 650 MPs sat in Parliament; it is delivered by thousands of Conservative councillors up and down the country who deliver elections for the party.”